The invention relates to backlight modules, and in particular to backlight modules having diffraction optical elements to control light distribution and light intensity of backlight modules.
Currently, in order to distribute light of conventional LED backlight modules, specially designed lens caps are provided. U.S. Pat. No. 6,679,621 B2 LUMILEDS discloses a side-emitting LED backlight module, wherein a special optical lens cap is disposed on the side-emitting LED backlight module to enforce the effect of uniformly emitting light. The curvature of the lens cap is, however, limited by process resolution. Thus, lens cap production is difficult and the lens cap is thicker. Accordingly, the thickness of the backlight module will increase dramatically. Additionally, in the conventional direct backlight modules, the light emitted from the light source travels forward through the transparent plate to the diffuser and then uniformly distributes on the liquid crystal display via the diffuser. However, due to the insufficient penetrability of the transparent plate and the consideration of the uniform light distribution, the thickness of the backlight module cannot be reduced due to multilayer arrangement.